Transformer oil containing a tertiary alkyl phenol antioxidant and a dihydroxy anthraquinone as a synergist for the antioxidant



Patented Mar. 16, 1954 TRANSFORMER OIL CONTAINING A TERTI- ARY ALKYL PHENOL ANTIOXIDANT AND A DIHYDROXY ANTHRAQUINONE AS A SYNERGIST FOR THE ANTIOXIDANT Charles D. Newnan, San Pablo, and Neal W. Furby, Berkeley, Calif., assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware No'Drawing. Application September 27, 1952, Serial No..31l,944

11 Claims. (Cl. 25264) 1 This invention relates to the stabilization of lubricating oil compositions intended for use in the service of transformer oils, turbine oils, and the like. More particularly, this invention pertains to mineral oil compositions useful as trans- 5 conjuntcion with a less refined lubricating oil. former oils, wherein the antioxidation charac- In attempting to increase the oxidation stabilteristics of the antioxidant present in the comity of transformer and turbine oils, known oxidaposition (e. g., 2,6-di-tertiary butyl-i-methyl tion inhbiitors (e. g., 2,6-di-tertiary butyliphenol) have been enhanced by the presence of methyl phenol) were incorporated therein, and, hydroxyanthraquinone compounds (e. g., quias expected, the resulting compounded oils were nizarin). more resistant to oxidation than the base oils This patent application is a continuation-incontaining no inhibitors. However, it was not to part of Newnan-Furby application Serial No. be expected that the oxidation stability of the 159,141, filed April 29, 1950, now abandoned. oil thus compounded with oxidation inhibitors The efiectiveness of transformer oils as incould be increased still further by adding theresulating oils is materially reduced by the oxidato an agent which by itself is not an oxidation tion products (i. e., the acid products) formed. inhibitor. Furthermore, these acid products gradually at- It is an outstanding feature of this invention tack the insulation on the wires of the transthat the oxidation stability of a lubricating oil former system, leaving the wires partially excompounded with an oxidation inhibitor is maposed to the oil, which oil then serves as a transterally increased by adding thereto an agent not mitter of current instead of an inhibitor of curknown as an oxidation inhibitor which agent rent. In the turbine oils the oxidation products asserts synergistic efiects in combination with the (i. e., the acid sludges) corrode the bearings and oxidation inhibitors of this invention. other parts of the turbine system and clog the oil It is an object of this invention to incorporate lines, etc. in mineral oils containing oxidation inhibtors an It is a tremendous advantage in transformer, agent exhibiting a marked synergistic eifect on turbine, and like systems, to use the oils of sufcertain oxidation inhibitors. ficient oxidation stability to permit their use over It has been discovered that highly oxidation long periods of time without being changed. Not resistant lubricating oil compositions may be only is it desirable to have transformer oils and prepared by incorporating hydroxy anthrathe like highly resistant to oxidation, but it is quinones in lubricating oil compositions conalso a desired feature of the transformer oils taining phenyl hydroxy compounds as oxidation and the like that the viscosity index be high; inhibitors. that is. that n y small chang s n v sc s ty 0 The hydroxy anthraquinones of this invention our with large changes in temperature. Thus, in include anthraquinones containing two hydroxyl order to obtain oils of high viscosity index, the groups on the ring, such as exemplified by base oils are subjected to such effective methods alizarin (1,2-dihydroxy anthraquinone), quiniof refining as selective solvent extraction proczarin (1,4-dihydroxy anthraquinone), anthraesses wherein the lower viscosity index hydrocarruflin (1,5-dihydroxy anthraquinone), chrysazin bons are selectively dissolved. Selective solvent (1,8-dihydroxy anthraquinone), xanthopurpurin refining pr s s c nc ntrat in one frac on, (1,3-dihydroxy anthraquinone), hystazin (2,3-diusu y h undissolved O fraction. those O hydroxy anthraquinone), isoanthrafiavinic acid pounds of a paraflinic nature which show a (2,7-dihydroxy anthraquinone), etc. smaller change in viscosity upon ch in t m- The anthraquinones forming a part of the Perature- However. ly efi ed O ls h v composition of this invention also include smaller amounts of naturally occurring oxidation anthraquinones containing alkyl groups having inhibitors present in the oils than do less refined from 1 t ab t 13 carbon atoms, These alkyl- OilS. That is, naturally Occurring inhibitors have substituted anthraquinones include 3-buty1-1,2- 7 been removed at least to an extent which madihydroxy anthraquinone 3-penta-1 2-dihy terially reduces the oxidation stability of the oil droxy anthraquinone, 4-hexyl-1,2-dihydroxy when used as transformer oils and as turbine oils. anthraquinone, 3 t 1-1 i t When oxidationinhibitors are added'to highly quinone, 3-decy1-L2-dihydroxy anthraquinon'e, refined oils and oils which are not so highly re- 3-hexadecyl-1,2-dihydroxy anthraquinone, 3- fined, it is found that the highly refined oils are octadecyl-1,2-dihydroxy anthraquinone, 2-butylmore responsive to the oxidation inhibitors; that 1,3-dihydroxy anthraquinone, 2'-butyl-1,3-dihy- 2 is, when the oxidation inhibitors of this invention are incorporated in so-called over-refined oils, a greater resistance to oxidation is obtained than when the oxidation inhibitors are used in droxy anthraquinone, 2-butyl-1A-dihydroxy anthraquinone, Z-hexyl-lA-dihydroxy anthraquinone, 2-octyl-L4-dihydroxy 'anthraquinone, 2-decyl-1A-dihydroxy anthraquinone, 2-dodecyl- IA-dihydroxy anthraquinone, 2-hexadecyl-1A- dihydroxy anthraquinone, 2-octadecyl-1,l-dihydroxy anthraquinone, 2-eicosyl-lA-dihydroxy anthraquinone, 2-triacontyl-l,4-dihydroxy .anthraquinone, 2-nonyl-1,4-dihydroxy anthraquinone, 2-methyl-1,4-dihydroxy anthraquinone, Z-ethyl-IA-dihydroxy anthraquinone, 2-methyl- 1,5-dihydroxy anthraquinone, 2butyl-1,5-dihydroxy anthraquinone, 2-octyl-1,5-dihydroxy anthraquinone, 2-nonyl-1,5-dihydroxy anthraquinone, 2-octadecyl-1,5-dihydroxy anthraquinone, 2-triacontyl-1,5-dihydroxy anthraquinone, etc. The 1,4-clihydroxy anthraquinones and the 1,5-dihydroxy anthraquinones are especially preferred because these dihydroxy anthraquinones are more eifective in increasing the antioxidation effects of the phenyl hydroxy compounds as oxidation inhibitors of this invention.

Qxidation inhibitors which are contemplated by this invention to be used in viscous oil com positions in combination with the dihydroxy anthraquinones are the phenyl hydroxy compounds containing at least one hydroxyl group. That is, the oxidation inhibitors included herein are phenyl hydroxy (hydroxy phenyl) compounds containing one or more hydroxyl groups on the ring, preferably only one hydroxyl group on the ring.

When the phenyl hydroxy compound contains only one hydroxyl group, there can be from 1 to 5 alkyl groups present in the compound, the alkyl groups containing a total of from 3 to about carbon atoms. However, it is preferred that there be three alkyl groups present, at least one of the alkyl groups being a tertiary alkyl group. It is especially preferred to use phenyl hydroxy compounds containing only one hydroxyl group and containing three alkyl groups, two of which alkyl groups are tertiary alkyl groups, particularly tertiary butyl groups.

Examples of the various phenyl hydroxycompounds which are included in the present invention are: monotertiary butyl-meta-cresol, 2,6- ditertiary butyll-methyl phenol, 2,4-ditertiary butyl-fi-methyl phenol, 2,4,6-trimethyl phenol, 2,4,6-tritertiary butyl phenel, catechol, p-tertiary butyl catechol, resorcinol, Z-pentadecyl hydraquinone, etc.

The term alky as used herein means a saturated or unsaturated monovalent hydrocarbon radical; for example, methyl, ethyl, ethenyl, propyl, propenyl, tertiary butyl, secondary butyl, octenyl, pentenyl, decyl, decenyl, dodecyl, dodecenyl, hexadecyl, heptadecyl, etc.

The mineral oil constituents of the lubricating oil composition include such base oils as naphthenic base oil, parafiin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oil derived from coal products, and synthetic oils, e. g., alkylene polymers (such as polymers of propene, butene, etc., and mixtures thereof), alkylene oxide-type polymers (e.

propene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., propene oxide, in the presence of water or alcolol, e. g., ethyl alcohol, and esters of alkylene oxide-type polymers, e. g., acetylated prqpene mxide polymers prepared by acetylating propene .oxide polymers containing hydroxyl groups.

Other synthetic oils include 'dicarboxylic acid esters .of *polyhydric 'tol 'tetracaprate.

esters, polyesters, esters of polyhydric alcohols, and liquid esters of acids of phosphorus.

Synthetic oils of the dicarboxylic acid estertypeinclu'de those which'are prepared'by esterifying such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaricacid, maleic acid, etc., with alcohols :such as butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, Z-ethylhexyl alcohol, dodecyl alcohol, pentaerythritol, hexamethylene glycol, etc. Examples of dicarboxylic acid ester synthetic oils include dibutyl adipate, dihexyl adipate, ,di-2-ethylhexyl sebacate, condensation products of hexamethylene glycol and adipic acid, etc. Other synthetic oils include alcohols, e. g., pentaerythri- .Syntheti'c oils of the type of liquid esters of acids of phosphorus include the esters of phosphoric acid, e. g., tricresyliphosphate; the .esters of phosphonic.acid,.e.g., diethyl ester of decane phosphonic acid.

The oxidation inhibitors (i..e., the .phenyl hydroxy compounds) whichare present in the lubricating oil composition of this invention may be present in amountsfrom about 0.01% to about 3.0% by weight of the final composition, that is, an amount sufiicient .to increase the resistance of the lubricating oil composition to oxidation. It is preferred to use from about 0.1% to about 1.0% by weight, based on the finished composition.

The hydroxy anthraquinones-of this invention (e. g., quinizarin) may be present in the final mineral oil composition in amounts from about 0.0.02 to about 1.0% by weight of the finalcomposition. Itis preferred to .use an .amount sulficient to enhance the oxidationinhibiting characteristics of the phenyl hydroxy compound, preferably fromsabout 0.01% to about 0.1%.

In certain instances .(for example, for shipping purposes) it is more preferable to prepare lubricating oil concentrates .of the additives of this invention. That is, the phenyl hydroxy compounds of this invention can be present inlubrieating .oil compositions in amounts as great as 50% by weight of the final composition. The hydroxy anthraquinones can be present in such amounts as permitted by'their solubility in the base oil, which, in some instances, is more than 1 and in other instances is .less than 1%., even less than 0.5% by .weight.

It was wholly unexpected that the hydroxy anthraquinones be. g.,-.quinizarin) would exert such synergistic effects .upon the lubricating oil oxidation inhibitors .(i. e., the phenyl hydroxy compounds) :Nowhere would. anyone expect to find suchlsynergistic eflfects as disclosed herein by the addition'of a synergist (-i. e., a hydroxy anthraquinone) as asecorrdary agent to a lubricating oil composition containing additives which are known to inhibit oxidation, particularly to find these antioxidation properties enhanced so tremendously :by the addition .of a secondary agent which in itself has relatively no effect in inhibiting oxidation :in a lubricating oil. It is well known in the :art that the .phenyl hydroxy compounds are vremarkableoxidation inhibitors; but it is entirely new to discover this effect of the hydroxy anthraquinones on the oxidation inhihiting effects .of the phenyl hydroxy compounds. Dbviously, it iis not merely an additive effiect which is obtained between the combinations of the known nxidation inhibitorin the lubricatingoil and the hydroxy anthraquinone be- 6 cause the hydroxy anthraquinones in themselves are practically inefiective in inhibiting-the oxidation-of lubricating oil compositions.

droxy anthraquinone to a lubricating oil contain-- ing 0.3% by weight of monotertiary butyl meta- In the table hereinbelow, data are presented to cresol. show the synergistic effects obtained by testing TABLE III the compositions of additives in a lubricating oil under severe conditions. In order to test ef- Amt of Ame of fectively the compositions of this invention, a Pheflyl HYdYOXY more drastic test was devised than is normally Team), wtigfiliid 51533; $531125) used in evaluating transformer oils and the like. g fl f geef This test has been called the California Remg mg search Transformer Oil Stability Test. The test 21 24 (2) is run as follows: 7 "6:65' 25 A 300 gram sample to be tested is placed in a 3 2? glass tube which is set in an oil bath at 250 F.

Oxidation catalysts, i. e., 112 square centimeters of medium silicon transformer iron (such as U. S. S. Trancor '72) and 450 square centimeters of No. 14 gauge ASTM electrolytic copper wire These data show that hydroxy anthraquinones produce a synergistic effect in oils containing phenyl hydroxy compounds having one hydroxyl are inserted in th tube. Oxygen is bubbled group and at least two alkyl groups attached to the ring.

The data of Table IV hereinbelow illustrate the through the test sample at a rate of 3 liters per hour until the test sample has an acid number of 1.0 (milligrams of KOH per gram sample of oil). eifectiveness of other anthraquinones as syn- The number of hours required for the sample to ergists in enhancing the stability of oil composhow an acid number of 1.0 is known as the test sitions containing phenyl hydroxy compounds life" of the sample. according to applicants invention.

The data presented in Table I will serve to 11- TABLE IV lustrate the nature of the results that were obtained in accordance with the present invention.

Additive (percent by TABLE I Weight) Hydmxy Test Quinizarm m a mmeral 021 containing Test No. Anthm' 1.1m

2,6 Diterti- H d o quinone (H dztertzary butyZ-et-methyl phenol airlyfiBtlliltyll 5 5 Used e y Phenol qumone m Base er m7 Test Life Test No. on Butyl-4- Q inizarin (Hours) 25 :3

Methyl Phenol 25 s15 20 egg 25 so 185 104 155 130 2(3,5,5-trimethy1-l-hexyl) qyinizarin prepared by the reaction 24 aqueous sodium hydroxide and sodium hyposulfide at 95 2Q 1,6-dihydroxyanthraquinone.

1,8-d1hydroxy anthraqumone. 24 A combination of additives of the present in- 20 vention are used efiectively not only in transform- 400 er oils, turbine oils and the like, but are also used efiectively in hydraulic oils, ice machine oils,

instrument oils, etc.

Other groups of additives may also be used in the oils in addition to the components of this invention. For example, in addition to the abovenoted compounds, the lubricating oils may contain other agents such as pour point depressants, oiliness agents, extreme pressur agents, blooming agents, compounds for enhancing the vissocity index of hydrocarbon oils, grease-forming agents, Peptizing agents, etc.

We claim: 1. A transformer oil consisting essentially of a major portion of a lubricating oil and a minor portion of a combination of a tertiary alkyl 5 phenol antioxidant for saidlubricating oil and a synergist for said antioxidant, said antioxidant being present in an amount suflicient to increase the resistance of said oil to oxidation, said synergist being a hydroxy anthraquinone selected from the group consisting of alizarin, quinizarin,

230 of quinizarin and 3,5,5-trimethyi hexaldehyde in the paesence of oil (2) of Table I hereinabove.

TABLE II Nonyl quim'zarin in a mineral oil containing 0.3% 2,6-dz'tertiary butyZ-4-meth1ll phenol N onyl Quinizarin Test Life (Percent by (Hours) Weight) Test No.

17::::::::::::::::::::::::::::::::::":::: 0.005 aim anthrarufin, chrysazin, and 2-methyl-1,4-dihy- 3:111:11::::::::::::::::::::::::: 8132 Z33 droxy anthraquinone. id synergist being pres- 20 0 10 800 ent in the proportion of about 0.002% to about 1.0% by weight of said transformer oil. The data set forth hereinbelow in Table III 2. The transformer oil of claim 1 in which show the effect of adding quinizarin as thehy- 

1. A TRANSFORMER OIL CONSISTING ESSENTIALLY OF A MAJOR PORTION OF A LUBRICATING OIL AND A MINOR PORTION OF A COMBINATION OF A TERTIARY ALKYL PHENOL ANTIOXIDANT, FOR SAID LUBRICATING OIL AND A SYNERGIST FOR SAID ANTIOXIDANT, SAID ANTIOXIDANT BEING PRESENT IN AN AMOUNT SUFFICIENT TO INCREASE THE RESISTANCE OF SAID OIL TO OXIDATION, SAID SYNERGIST BEING A HYDROXY ANTHRAQUINONE SELECTED FROM THE GROUP CONSISTING OF ALIZARIN, QUINIZARIN, ANTHRARUFIN, CHRYSAZIN, AND 2-EMTHYL-1,4-DIHYDROXY ANTHRAQUINONE, SAID SYNERGIST BEING PRESENT IN THE PROPORTION OF ABOUT 0.002% TO ABOUT 1.0% BY WEIGHT OF SAID TRANSFORMER OIL. 